One of the greatest scientific achievements of the 20th century should now be attributed to a black man, or so it seems.

James Watson, the man who worked with Francis Crick to identify the double-helical structure of DNA, who upon casual inspection might well qualify for the title of "most blatantly Caucasian male" among a raft of serious contenders that includes Mitt Romney, Tucker Carlson, Harry Reid and Peyton Manning, is actually black!

An Iceland-based genomics company, deCODE genetics, conducted an analysis of Watson's DNA, which Watson had allowed to be placed on the Internet, and found that 16 percent of his genes are likely to have come from a black ancestor.

The flamboyant head of deCODE, Kari Stefansson, himself a strong contender for the most obviously Caucasian male award, whose company carried out the analysis, said in a classic bit of white male understatement, “It was very surprising to get this result for Jim.”

Indeed, the racial outing of Watson was quite a surprise — most likely to the 79-year-old Nobel-prize winner. This past October he was forced to cancel a tour promoting his new book in England after opining in a British newspaper that he felt “inherently gloomy about the prospects for Africa” because “all our social policies are based on the fact that their intelligence is the same as ours — whereas all the testing says not really.” Jim’s fretting left him without a job at home — he retired from his job as chancellor at the Cold Spring Harbor Laboratory in New York — and no longer especially welcome on the speaking circuit anywhere serious. Finding out one has black genes seems especially inconvenient for somebody proclaiming blacks to be genetically inferior.

Watson’s critics are piling on with glee to such delicious irony. But while it is more than tempting to use this incident to bury the influential source of some very irresponsible racial speculation (yeah, OK, I have been indulging myself in the temptation) a number of other more important lessons need to be drawn from the news of Watson’s reclassification in the family of man.

First, our ordinary racial categories do not have much scientific meaning. They are social and cultural creations.

Those classified as black or white in the United States would not always be considered so in Brazil, South Africa, Tonga, India, Japan or Mexico. The differences people in China, Myanmar, Nigeria or India see among various ethnic groups are quite different from the classifications that ordinary Americans or Canadians might make of the same people.

Genetic groupings of people that scientists use in designing drugs or studying migration patterns do not overlap with the groupings that North Americans make of people based on their skin color, hair or other features.

Nor is it at all useful to try and determine your race or ethnicity from your genes.

Genes change rapidly as they recombine generation after generation as a result of sex. So scientists look for markers on the most stable elements of our genome — the Y chromosome, most of which you get only from your dad, or mitochondrial DNA, most of which you get only from your mom. The stability comes at a price. Those genes represent a very narrow glimpse of your distant ancestors because only a few of their contributions are reflected in these particular packets of DNA. The potential for errors in trying to classify people using these markers into groups that don’t make much biological sense anyway is, to say the least, huge.

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So forget plunking your money down with one of the many companies offering genetic analysis of your family tree. You will only wind up, as Watson did, with a classification based on a tiny handful of those who were actually your ancestors.

And most of the ability at present to analyze genes comes from comparing them to samples that have been collected and made public by various scientists and companies. But the sampling is far from complete so most genetic analysis for complex traits and behaviors including race is based on incomplete data.

So while it is extremely amusing (to me at least) to revel in the irony that somebody who got into trouble for racist remarks might himself be a member of the very group he was impugning, as a matter of science it is nonsense.

Science is not in a position to tell you who your ancestors were in terms of race both because our knowledge of their genetics is very limited and the classifications we use to put people into groups vary from culture to culture, time period to time period and nation to nation.

Watson, a great scientist, despite his most recent ranting about race, knew right after his discovery, and better than anyone, how complex the story of heredity actually is. It would be a grave mistake to think that peeking at our genes will tell us something about who we truly are in terms of race. There has been too much hatred, bias and prejudice in human history to think that your race is simply a matter of examining your genes.

Arthur Caplan, Ph.D., is director of the Center for Bioethics at the University of Pennsylvania.